I shot and chronographed four different loads in regular ACP brass with large pistol primer, in NT brass with small pistol primer, and in NT brass with small pistol magnum primer.
The SP primer gave 20-50 fps lower velocity than the LP with same powder charge and bullet.
The SP Magnum primer made up part or all of the velocity loss, or even increased velocity over LP in one case, HS6 & 185gr JHP.
[I have done some primer comparisons in 9mm and a small pistol magnum gives higher velocity than a small rifle standard.]
Shoudek,
They DID make large pistol NT ammo for a while, it is the brass with extra large flashhole. Winchester says that is ok to reload, and I don't even sort that out.
But they changed to small, either due to technical considerations - I have seen two or three explanations, but none from Winchester - or maybe they are trying to make things hard on handloaders so we will give up and buy more factory loads.